The mother of the 22-month-old who died after being left inside a hot SUV told police she also researched children dying in hot vehicles, according to new court documents released.

"Leanna Harris, the child's mother, was also questioned regarding the incident and made similar statements regarding researching in car deaths and how it occurs," search warrant affidavits obtained by The Atlanta Journal-Constitution state.

The timing of those online searches and investigators' findings have not been released. But within about five hours of the toddler's death on June 18, his father, Justin Ross Harris, was arrested and charged with murder and cruelty to children.

Leanna Harris has not been identified as a suspect in the death of her son, Cooper. But she was also questioned in the hours after the boy's death after he was left in his carseat inside a Hyundai Tucson for at least seven hours while his father went to work.

On Saturday, Leanna Harris spoke at her son's funeral - as did Ross Harris, by telephone.

"Am I angry with Ross? Absolutely not," said Leanna Harris, who remained composed throughout the eulogy. "It never crossed my mind. Ross is and was a wonderful father."

In brief remarks made over the phone, Ross Harris thanked those who continue to believe in him.

"(Cooper) never did anything to anyone," he said, audibly choked up. "I'm just sorry I can't be there."

Cooper's death and his father's subsequent arrest quickly made headlines worldwide, sparked by a sharply divided debate over whether the felony charges were appropriate. Support for Ross Harris, including an online petition to the Cobb County District Attorney, has shifted in recent days as new facts in the case have been reported. The online petition was halted Wednesday after more than 11,000 people had signed in support of charges being dropped in the case.

The boy's father told police he had searched online for information regarding temperatures needed for children to die inside vehicles because he was "fearful" it could happen, according to search warrant affidavits released Saturday.

Additional affidavits released Sunday state that Leanna Harris made similar statements. Police seized several electronics from the SUV and the couple's Marietta-area condo, including an iPhone, iPad, a desktop computer, two laptops and a Google Chromecast digital media player, the warrants state.

The findings and evidence cited to arrest the boy's father were not released and may not be until a possible trial. By law, after applying for search warrants, investigators have 10 days to conduct the searches and return the application documents to Magistrate Court.

On the morning of June 18, Ross Harris and Cooper had breakfast at a Vinings Chick-fil-A before the father strapped his son into a rear-facing carseat in the backseat of the SUV, according to police. From there, Harris drove less than a mile to his Home Depot office and went to work, leaving Cooper inside the vehicle, warrants state.

Harris went back to his SUV at lunchtime and put something inside through the driver's side door. But it was not until after 4pm when he was leaving work to meet friends that Harris said he realised his son was still in the backseat, police have said. He told police he immediately pulled into an Akers Mill Road shopping center for help.

"Oh my god what have I done," Harris screamed, according to witnesses. Harris placed the boy on the parking lot pavement and began to administer CPR on him as witnesses gathered and also tried to help revive Cooper.

"When someone came to assist Justin he stopped providing medical attention to the child and started making calls on his cell phone," the affidavits state.

Cooper was pronounced dead in the parking lot. An autopsy later determined that he died from hyperthermia, or elevated body temperature, according to police. It was 31 degrees Celsius at 5.16 pm on June 18.